Such a shoulder prosthesis is known from EP-A 0 953 321. The middle section has outwardly-projecting ribs by means of which it can be inserted into a recess at the proximal end of the stem in various laterally-medially staggered positions. The middle section is connected to the stem by a press fit and the ball head has a recess of constant cross-section by means of which it is fitted onto the middle section. The middle section is angled as a result of which various inclinations and retroversion angles can be set.
A shoulder prosthesis is known from U.S. Pat. No. 5,961,555 in which the middle section can be fitted onto a cone at the proximal end of the stem and the ball head is clamped by means of a conical dovetail guide. Apart from the fact that the ball head is displaced in anterior-posterior direction when clamped to the middle section, the ball head is not adjustable vis-à-vis the stem.
Shoulder prostheses in which the middle section is conically developed at both ends and can thereby be connected to the stem and the ball head are known from EP-A-0 549 480, EP-A 0 599 429, FR-A 2 721 200 and U.S. Pat. No. 6,197,062. The axes of both conical ends are angled vis-à-vis each other and/or offset vis-à-vis each other as a result of which a lateral-medial and posterior-anterior adjustment of the ball head and optionally of the retroversion angle vis-à-vis the stem is possible. A similar shoulder prosthesis is also known from DE-A 198 41 612, the middle section being disk-shaped and having axial pins, offset vis-à-vis each other, on both sides.
A shoulder prosthesis in which the middle section has a cylindrical section, the axis of which runs parallel to the stem axis and which can be clamped to the proximal end of the stem with adjustable rotation position, is known from EP-A 0 679 375. Projecting from this cylindrical section is a conical section onto which the ball head can be fitted.
Shoulder prostheses in which the middle section can be adjusted vis-à-vis the stem by means of a ball-and-socket joint, the concave surface of the ball-and-socket joint being developed in the stem, are known from EP-A 0 712 617, U.S. Pat. No. 6,228,120 and U.S. Pat. No. 6,206,925. In the case of the shoulder prosthesis known from EP-A 0 715 836, the concave surface of the ball-and-socket joint is developed in the ball head and the joint ball added at the proximal stem end.
Shoulder prostheses in which the middle section is adjustable at the proximal end of the stem in the direction of the stem axis, as a result of which the effective length of the prosthesis stem can be altered, are known from DE-A-195 48 154 and DE-U-299 18 669.
A shoulder prosthesis in which the distance between ball head and stem can be altered by providing the ball head with an axial or axis-parallel threaded section that can be screwed into a threaded bore at the proximal end of the stem is known from DE-U-93 12 218. The ball head can be fixed by means of a safety screw that can be screwed in transversely thereto.